.TH std::basic_fstream::is_open 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::basic_fstream::is_open \- std::basic_fstream::is_open

.SH Synopsis
   bool is_open() const;

   Checks if the file stream has an associated file.

   Effectively calls rdbuf()->is_open().

.SH Parameters

   \fI(none)\fP

.SH Return value

   true if the file stream has an associated file, false otherwise.

.SH Example


// Run this code

 #include <fstream>
 #include <iostream>
 #include <string>

 int main()
 {
     std::string filename = "some_file";

     std::fstream fs(filename, std::ios::in);

     std::cout << std::boolalpha;
     std::cout << "fs.is_open() = " << fs.is_open() << '\\n';

     if (!fs.is_open())
     {
         fs.clear();
         fs.open(filename, std::ios::out);
         std::cout << "fs.is_open() = " << fs.is_open() << '\\n';
     }
 }

.SH Possible output:

 fs.is_open() = false
 fs.is_open() = true

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

     DR    Applied to             Behavior as published              Correct behavior
   LWG 365 C++98      is_open was not declared with const qualifier declared with const
                                                                    qualifier

.SH See also

   open  opens a file and associates it with the stream
         \fI(public member function)\fP
   close closes the associated file
         \fI(public member function)\fP
